The present invention relates to a method and apparatus to reduce overshoot and undershoot voltages (e.g., spike voltages) in class D amplifiers and DC-DC converters like boost converter or buck converters.
High efficiency therefore low heat dissipation and long battery life can be achieved by using switched output stage in audio amplifiers like class D amplifiers. A Class D amplifier usually comprises of two switches, one is connected between power supply and output, another switch is connected between ground and output. By switching output either to power supply or ground, a string of high and low pulses are created at the output of class D amplifier, while a continuous output is constructed by filtering the class D amplifier output through a low pass filter, which can be implemented either explicitly or implemented within a load device like an audio speaker.
When using class D amplifier to drive a speaker, which can be deemed as a big inductive load, load current cannot change instantaneously. When both of the power switches are off, current can only go through the FET parasitic diode. Depending on the current direction, the parasitic diode can cause output to either be one diode-drop above power supply or one diode-drop below ground. When both of the power switches are on at the same time, shoot through current will cause power waste and large amounts of ringing at the output because of the abrupt change of current caused on parasitic inductance. Therefore, it is desirable to turn on the two switches in a switched output stage in a non-overlapped way but with overlap time as small as possible.